Mosquito-Borne Diseases in Toronto: GTA Risks
By PestRecord Editorial Team
Ready to enjoy your backyard without mosquitoes? Get free quotes from licensed mosquito control operators across the GTA.
Every summer, the headlines appear. West Nile Virus detected in Toronto mosquitoes. Your neighbour shares an article on Facebook. It sounds scary. But what is the actual risk, and what should GTA homeowners do about it?
The Facts About West Nile Virus
West Nile Virus (WNV) is spread through the bite of an infected mosquito. It was first detected in North America in 1999 and has been found in Ontario mosquitoes since 2001.
The reality:
- About 80% of infected people have no symptoms
- About 20% develop mild flu-like symptoms
- Less than 1% develop severe illness
- Severe cases typically affect older adults and those with compromised immune systems
- Deaths from WNV are rare in Ontario
The risk is real but low. Compared to the United States, Ontario has very few human cases. Toronto Public Health monitors mosquito populations and reports findings throughout the summer.
Where WNV Has Been Found
West Nile positive mosquitoes have been found across the GTA, particularly in:
- The Don Valley and surrounding areas
- The Humber River watershed
- The Rouge River area
- Parts of Mississauga and Brampton
- Various pockets throughout the city
The City of Toronto and regional municipalities conduct their own mosquito monitoring and larvicide programs.
What Professional Mosquito Control Does
Professional mosquito control involves two main approaches:
1. Larvicide Treatment
Bti (Bacillus thuringiensis israelensis) is a naturally occurring bacteria that kills mosquito larvae. It is applied to standing water sources, particularly catch basins, where mosquitoes lay their eggs.
Bti is safe: It only affects mosquito larvae. It is used in drinking water treatment and is safe for humans, pets, fish, and beneficial insects.
2. Barrier Spray
Professional barrier sprays are applied to vegetation around the perimeter of your property. The residual spray kills mosquitoes that contact the treated surfaces.
Effectiveness: Barrier sprays reduce mosquito populations by 80-90% around treated areas. The effect lasts 2 to 4 weeks.
When to Start
Timing matters:
- May: Larvicide treatment in catch basins. This is the most important timing because it kills mosquitoes before they mature.
- June: First barrier spray application.
- July-September: Continue barrier spray treatments every 2-4 weeks through peak season.
Catch Basins: The Number One Breeding Source
Every street in the GTA has catch basins (storm drains). They are the number one breeding ground for urban mosquitoes. Water sits in them, they are rarely disturbed, and they produce millions of mosquitoes each summer.
Your municipality treats major catch basins, but property owners should treat private drains and those on their property.
What You Can Do
- Eliminate standing water on your property
- Change bird bath water weekly
- Clean eaves troughs
- Cover or treat decorative water features
- Use fan screens on windows
- Wear EPA-registered repellent when outdoors at dawn/dusk
- Wear long sleeves at dawn and dusk
Cost of Professional Treatment
- Initial treatment: $150 to $300
- Seasonal program (3-4 visits): $300 to $600
- Large properties: $500 to $1,000+
Frequently Asked Questions
Is West Nile Virus a real threat in Toronto?
West Nile Virus has been detected, but the risk is low. Most people infected have no symptoms.
Where has West Nile been found in the GTA?
West Nile positive mosquitoes have been found in the Don Valley, Humber River, and Rouge River areas.
Does professional mosquito control work?
Yes. Barrier sprays reduce mosquito populations by 80-90%. Bti larvicide kills larvae before they mature.
When should I start mosquito control in the GTA?
Start in May with larvicide treatment. Barrier spray in June provides ongoing protection.
How much does professional mosquito control cost in the GTA?
Professional mosquito control runs $150 to $300 for initial treatment, with seasonal programs running $300 to $600.
Want to enjoy your backyard this summer? Get free quotes from licensed mosquito control operators today.